1. Field of the Invention
The present invention is directed to a dental handpiece, which has a grip section, which has a head section at one end for supporting a working instrument, such as a dental burr or drill, for rotation, and is coupled for relative rotation to a drive section containing a motor for rotating the dental instrument. The dental handpiece has at least one coolant line for supplying a coolant for discharge to the area of the dental instrument and each coolant line is formed by passages in the drive section and grip section which are interconnected as the grip section is coupled onto the drive section.
2. Prior Art
A dental handpiece, which has a grip section, which is coupled onto a drive section for relative rotation with the grip and drive sections having passages coacting to form at least one coolant line for conveying a cooling medium to the area of a dental instrument, is disclosed in U.S. Pat. No. 3,936,940. In this handpiece, a connection between the passages of the drive section and grip section is formed by an annular groove provided in one of the two sections, which is in communication with a port in the other section and the connection is sealed by a pair of O-rings received in O-ring grooves. In the patent, two embodiments of the fluid connection provide the port, the annular or ring groove and the O-rings on parts which are telescopically received on each other during the connection of the grip section to the drive section. In the third embodiment, the fluid connection is formed by the annular groove, port and the O-ring grooves and O-rings being disposed on plane surfaces, which extend radially to the axis of the drive shaft of the drive section. In each embodiment, the O-rings are carried on the drive section and the coupling and decoupling of the grip section onto the drive section connects and disconnects the rotatable connection.
Thus, in the handpiece such as disclosed in this U.S. patent, the O-rings are subjected to stresses during the coupling and decoupling of a grip section from the drive section and in several embodiments, the O-rings are also subjected to a twisting stress. Since a dentist as a rule will utilize a single drive section for a dental handpiece with several different grip sections, which have different gearing arrangement to either step up or step down the speed or rotation for the tool, the drive section is thus the most frequently used part. Thus, the sealing rings, which are carried on the drive section, are subjected to stresses occurring during coupling and decoupling of each grip section on the drive section. Since coupling and decoupling of the grip section frequently occurs, the sealing rings are subjected to particularly heavy wear, which can lead to leaks occurring at the connection between the passages after a relatively short time. While one may compensate for this problem with an increase of an initial radial tension on the sealing rings, such an increase would also increase the friction between the two rotatable sections and thus decrease the rotatability of the grip section on the drive section.
Since one may couple a grip section of an old construction with a drive section, which is provided with a cooling medium connection adjacent to the guide member, even greater wear of the sealing rings may occur. For example, grip sections of an older type often do not have beveled or chamfered edges to facilitate their mounting on the guide member and thus these older type grip sections will increase the wear or chance of damage to the sealing rings on the drive section.
In addition to the disadvantages of relatively heavy wear of the sealing rings in the previously known type of handpiece, the occurrence of a leak due to wear may not be recognized by the user of the handpiece. While a leakage at one of the two sealing rings will allow the liquid to flow to an external surface to be noticed, leakage at the other ring will allow the cooling medium to penetrate into the interior of either the grip section or the drive section and thus into portions of the drive train such as bearings of the drive train without the operator being aware of such a leak.
An additional disadvantage of the rotatable connection of the dental handpiece of the above mentioned patent is the fact that while the grip section is disconnected from the drive section, the sealing rings are not protected against soiling or other damage. This danger particularly exists when the grip section has been uncoupled from the drive section for a long time, which would occur while sterilizing the grip section or while storing the grip section in a sterile condition.